Processing of polypropylene and products therefrom

ABSTRACT

A method for producing a low viscosity polypropylene composition may include melting a polypropylene-based composition; reducing a viscosity of the polypropylene-based composition; and optionally, repeating the melting and the reducing steps to form a low melt viscosity polypropylene-based composition; wherein the melting and viscosity decreasing steps are performed in the presence of at least one free radical generator and at least one pro-degradant stearate.

BACKGROUND

Polyolefins such as polyethylene (PE) and polypropylene (PP) may be usedto manufacture a varied range of articles, including films, moldedproducts, foams, and the like. Polyolefins may have characteristics suchas high processability, low production cost, flexibility, low densityand recycling possibility. While plastics such as polyethylene andpolypropylene have many beneficial uses, there is a need for theircorrect disposal after use, or even their reuse or recycling so as tominimize the environmental impact of plastic wastes.

One of the largest challenges faced by society today is to reducegreenhouse gas emissions in order to minimize the anthropogenic impacton the climate and environment. Governmental regulations may set limitson CO₂ emissions and drive the transition to a low carbon economy basedon renewable energy, in addition to the development of new economic andbusiness models. In some cases, new production techniques and materialsolutions may be necessary to reduce the carbon footprint of plasticmanufacture.

A part of this approach is reconsidering the use of plastics in order toreduce the environmental impact of plastic waste. One option is torecycle the consumed plastic and reintroduce it in the plastic valuechain. Consumed plastics, such as post-consumer resins (PCR), areavailable in the market, but because of the high inhomogeneity ofsources and the chemical and mechanical damage that the plastic hasendured (from production to waste), the properties of these resins aregenerally poor, and it is a challenge to reuse them in many applicationsthat require high property standards.

In this connection, a process to reduce the viscosity of polypropylenewould be particularly beneficial in the circular economy field as itwould broaden the application of post-consumed or post-industrialplastics.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments disclosed herein relate to a method forproducing a low viscosity polypropylene-based composition that includesmelting a polypropylene-based composition; reducing a viscosity of thepolypropylene; and optionally, repeating the melting and the reducingsteps to form a low melt viscosity polypropylene; wherein the meltingand reducing steps are performed in a continuous process in the presenceof at least one free radical generator and at least one pro-degradantstearate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a frequency sweep analysis.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to methods ofprocessing a polypropylene-based resin to provide low viscositypolypropylene-based compositions that are useful for severalapplications, for instance, meltblown applications, chemical recyclingprocesses, among others.

Polypropylene-Based Compositions

The “polypropylene-based compositions” according to the presentdisclosure are polymer compositions comprising greater than 50 wt. % ofpolypropylene resin.

In one or more embodiments, the polypropylene-based compositioncomprises greater than 97 wt %, 98 wt. %, 99 wt. % or 100 wt. % ofpolypropylene based on the polymer content.

In one or more embodiments, the polypropylene-based composition is ablend of polypropylene resin and other olefin-based resins, wherein theolefin-based resin is present in an amount having a lower limit of about0.1 wt. %, 5 wt. %, 10 wt. %, 15 wt. %, 20 wt. % or 25 wt. %, and aupper limit of 30 wt. %, 35 wt. %, 40 wt. %, 45 wt. % or 49 wt. %,wherein any lower limit may be combined with any upper limit, whereinthe amounts are based on the sum of the polypropylene and olefin-basedresins weights. In a preferred embodiment, the blend comprises fromabout 0 to 49% of polyethylene, based on the sum of polypropylene andpolyethylene weight. In some embodiments, the olefin-based resins may beselected from polyethylenes, polybutylenes, ethylene-vinyl acetatecopolymers, polystyrenes, and combinations thereof.

The “polypropylene resin” or “PP” according to the present disclosureare polymers comprising greater than 50 wt. % of propylene monomer. ThePP may be selected from homopolymers, random copolymers, heterophasiccopolymers, heterophasic random copolymers, terpolymers and mixturesthereof. In some embodiments, the copolymers may contain comonomersselected from ethylene and alpha-olefins with 4 to 10 carbon atoms.

In one or more embodiments, the polypropylene resin and olefin-basedresins of the present disclosure may be selected from petroleum-basedresins, biobased resins and combinations thereof.

In one or more embodiments, the polypropylene resin and olefin-basedresins of the present invention may be selected from virgin resins,recycled resins and combinations thereof.

In one or more embodiments, the polypropylene-based composition maycomprise combination of recycled resins, biobased resins and optionallypetroleum based resins such that the resulting composition achieves lowor neutral carbon emission (or even a carbon uptake).

The recycled resin may comprise one or more selected from apost-consumer resin (PCR) and a post-industrial resin (PIR), includingregrind, scraps and defective articles. PCR refers to resins that arerecycled after consumer use, whereas PIR refers to resins that arerecycled from industrial materials and/or processes (for example,cuttings of materials used in making other articles). In one or moreembodiments of the present disclosure, the recycled resin used may be aPCR that comprises one or more polyolefins. In one or more embodiments,the recycled resin is a recycled material according to ISO 14021. Therecycled resin of one or more embodiments may include resins having beenused in rigid applications (such as from blow molded articles, including3D-shaped articles) as well as in flexible applications (such as fromfilms). The recycled resin of one or more embodiments may be of anycolor, including, but not limited to, black, white, or grey, dependingon the color used in the ultimate article. The form of the recycledresin is not particularly limited, and may be one or more of pellets,flakes, and agglomerated films.

In one or more embodiments, the polypropylene-based composition may havea viscosity of 200 to 130,000 Pa·s at 180° C. and 0.1 rad/s, measuredaccording to ASTM: D-4440-15 (Dynamic Mechanical Properties MeltRheology), prior to the processing method of the present invention. Inone or more embodiments, polypropylene-based composition may have aviscosity having a lower limit of any of 200, 300, 500, or 1000 Pa·s at0.1 rad/s to an upper limit of any of 15,000, 20,000, 50,000, 100,000,or 130,000 Pa·s at 0.1 rad/s.

In one or more embodiments, the polypropylene-based composition may havea melt flow rate varying from 0.1 to 35 g/10 min, as measure accordingto ASTM D1238 (2.16 Kg at 230° C.), prior to the processing method ofthe present invention.

Processing Method Description

The method for producing a low viscosity polypropylene-based accordingto the present disclosure comprises the following steps:

-   -   melting a polypropylene-based composition;    -   decreasing a viscosity of the polypropylene-based composition;        and    -   optionally, repeating the melting and the viscosity decreasing        steps to form a low melt viscosity polypropylene-based        composition;        wherein the melting and viscosity decreasing steps are performed        in the presence of at least one free radical generator and at        least one pro-degradant stearate.

In one or more embodiments, the melting and viscosity decreasing stepsare performed at temperature that is equal to or less than about 350°C., preferably around 200° C. to 250° C. This temperature may be thetemperature set up on the equipment (e.g. extruder).

In one or more embodiments, the melting and viscosity decreasing stepsare performed in residence time less than around 2 min, preferablyranges of less than 90 s.

In one or more embodiments, the method for producing a low viscositypolypropylene-based is performed in a continuous process, such as in anextrusion. In some embodiments, the method involves melting apolypropylene-based composition in an extruder, decreasing the viscosityof the polypropylene-based composition, and extruding the melt through adie. In accordance with one or more embodiments, the melting andviscosity decreasing may be repeated.

In case an extruder is used, it may be selected from a single-, twin-,or multi-screw extruder, in particular embodiments, a twin-screwextruder is used.

The processes of one or more embodiments of the present disclosureresult in the viscosity of the polypropylene-based compositiondecreasing in the extruder. In one or more embodiments, the process mayinvolve multiple extrusions in series, each of which sequentiallyreduces the viscosity of the recycled resin. The processes of one ormore embodiments may include one extrusion or more, or two extrusions ormore. In embodiments where multiple extrusions are performed, eachextrusion may be performed under conditions that are the same as, ordifferent from one another. In one or more embodiments, the melting andviscosity decreasing steps are performed in a continuous loop system.

In one or more embodiments, the at least one free radical generator maycomprise a peroxide. The peroxide of some embodiments may be one or moreof the group consisting of 3-hydroxy-1,1-dimethylbutylperoxyneodecanoate, a-cumyl peroxyneodecanoate,2-hydroxy-1,1-dimethylbutyl peroxyneoheptanoate a-cumylperoxyneoheptanoate, t-amyl peroxyneodecanoate, t-butylperoxyneodecanoate, di(2-ethylhexyl) peroxydicarbonate, di(n-propyl)peroxydicarbonate, di(sec-butyl) peroxydicarbonate, t-butylperoxyneoheptanoate, t-amyl peroxypivalate, t-butyl peroxypivalate,diisononanoyl peroxide, didodecanoyl peroxide,3-hydroxy-1,1-dimethylbutylperoxy-2-ethylhexanoate, didecanoyl peroxide,2,2′-azobis(isobutyronitrile), di(3-carboxypropionyl) peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, dibenzoyl peroxide,t-amylperoxy 2-ethylhexanoate, t-butylperoxy 2-ethylhexanoate, t-butylperoxyisobutyrate, t-butyl peroxy-(cis-3-carboxy)propenoate,1,1-di(t-amylperoxy)cyclohexane,1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, OO-t-amyl O-(2-ethylhexyl) monoperoxycarbonate, OO-t-butylO-isopropyl monoperoxycarbonate, OO-t-butyl O-(2-ethylhexyl)monoperoxycarbonate, polyether tetrakis(t-butylperoxycarbonate),2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-amyl peroxyacetate, t-amylperoxybenzoate, t-butyl peroxyisononanoate, t-butyl peroxyacetate,t-butyl peroxybenzoate, di-t-butyl diperoxyphthalate,2,2-di(t-butylperoxy)butane, 2,2-di(t-amylperoxy)propane, n-butyl4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-amylperoxy)butyrate, ethyl3,3-di(t-butylperoxy)butyrate, dicumyl peroxide,a,a′-bis(t-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy) hexane, di(t-amyl) peroxide, t-butyla-cumyl peroxide, di(t-butyl) peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, dicetil peroxi-dicarbonato,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane, tert-butylperoxy2-ethylhexyl carbonate, tert-butyl-peroxide n-butyl fumarate(benzoate),dimyristoyl peroxydiicarbonate, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane,tert-butyl hydroperoxide, bis(4-t-butylcyclohexyl) peroxydicarbonate,and 1,2,4,5,7,8-hexoxonane, 3,6,9-trimethyl-3,6,9-tris(ethyl and propylderivatives).

In one or more embodiments, the at least one free radical generator maybe a low-reactivity organic peroxide. The expression “low-reactivityorganic peroxide” is understood to be peroxides that have a 1 hourhalf-life temperature greater than or equal to 165° C. Some examplesinclude 3,3,5,7,7-Pentamethyl-1,2,4-trioxepane, terc-butylhydroperoxide, cumyl hidroperoxide, t-amyl hidroperoxide, or mixturesthereof.

In one or more embodiments, the at least one free radical generator maybe added to the polypropylene-based composition in an amount rangingfrom a lower limit selected from one of around 0.01, 0.1, or 0.2 wt. %to an upper limit selected from one of around 1, 1.25, or 1.5 wt. %,relative to the weight of the polypropylene-based composition, where anylower limit can be used with any upper limit.

In one or more embodiments, the polypropylene-based composition is alsoin the presence of a further at least one free radical generatorcomprising a nitroxide compound, such as2,2,5,5-tetramethyl-1-pyrrolidinyloxy,3-carboxy-2,2,5,5-tetramethyl-pyrrolidinyloxy,2,2,6,6-tetramethyl-1-piperidinyloxy,4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy,4-methoxy-2,2,6,6-tetramethyl-1-piperidinyloxy,4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy,bis-(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)sebacate,2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl)monophosphonate,N-tert-butyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide,N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide,N-tert-butyl-1-di(2,2,2-trifluoroethyl)phosphono-2,2dimethylpropylnitroxide, N-tert-butyl-(1-diethylphosphono)-2-methyl-propyl nitroxide,N-(1-methylethyl)-1-cyclohexyl-1-(diethylphosphono) nitroxide,N-(1-phenylbenzyl)-(1-diethylphosphono)-1-methyl ethylnitroxide,N-phenyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide,N-phenyl-1-diethylphosphono-1-methyl ethyl nitroxide, N-(1-phenyl2-methyl propyl)-1-diethylphosphono-1-methyl ethyl nitroxide,N-tert-butyl-1-phenyl-2-methyl propyl nitroxide, andN-tert-butyl-1-(2-naphthyl)-2-methyl propyl nitroxide, or a mixturethereof. In such embodiments, the further at least one free radicalgenerator comprising a nitroxide compound is added to thepolypropylene-based composition in order to accelerate the beta scissionreaction catalyzed by the peroxide compound.

The further at least one free radical generator may be added to thepolypropylene-based composition in an amount ranging from a lower limitselected from one of 0.01, 0.1, or 0.2 wt. % to an upper limit selectedfrom one of 1, 1.25, or 1.5 wt. %, relative to the weight of thepolypropylene-based composition, where any lower limit can be used withany upper limit.

In one or more embodiments, the at least one pro-degradant stearate isselected from a group consisting of zinc stearate, tin stearate, iron(II) stearate, iron (III) stearate, cobalt stearate, manganese stearate,and any combinations thereof. Unexpectedly, in the present disclosure itwas found that the beneficial effect of adding the at least onepro-degradant stearate is to decrease the amount of the free radicalgenerator, e.g., a peroxide compound, needed in the processing methoddisclosed herein. Consequently, there is a lower VOC emission in themethod of the present disclosure.

In one or more embodiments, the at least one pro-degradant stearate maybe added to the polypropylene-based composition in an amount rangingfrom a lower limit selected from one of around 0.05 wt % or 0.1 wt. % toan upper limit selected from one of around 2.0 or 2.5 wt. % relative tothe weight of the polypropylene-based composition, where any lower limitcan be used with any upper limit.

Further possible additives include those conventionally known to aperson of ordinary skill in the art. Any of the aforementioned additivesmay be added at any stage of a multiple extrusion process, in asequential or simultaneous manner, independently from any order.

In case an extruder is used, the resins, free radical generators,pro-degradant stearates and other components, may be added to anextruder, either simultaneously or sequentially, into the main orsecondary feeder in the form of powder, granules, or flakes. In one ormore embodiments, methods may involve a single extrusion or multipleextrusions.

In one embodiment, the method of the present disclosure comprises twoextrusion passes wherein the at least one free radical generator isadded on the first pass and the at least one pro-degradant stearate isadded on the second pass.

As mentioned above, the polypropylene-based composition may have aviscosity of about 200 to 130,000 Pa·s at 180° C. and 0.1 rad/s prior tothe method of the present invention. After the one or more melting andviscosity decreasing steps of the present disclosure, the viscosity maybe reduced to achieve a viscosity of less than about 300 Pa·s at 180° C.and 0.1 rad/s. Depending on the starting viscosity, desired finalviscosity, and therefore extent of viscosity decreasing to achieve suchfinal viscosity, the melting and viscosity decreasing steps may occurmultiple times.

In addition, after the one or more melting and viscosity decreasingsteps of the present disclosure, the melt flow rate of the low viscositypolypropylene-based obtained by the processing method is greater thanabout 75 g/10 min, as measure according to ASTM D1238 (2.16 Kg at 230°C.). In one or more embodiments, the melt flow rate of the achieved lowviscosity polypropylene-based composition is greater than 150 g/10 min,preferably greater than 300 g/10 min, more preferably 600 g/10 min, mostpreferably greater than 1000 g/10 min, and most preferred greater than1,500 g/10 min.

The process may further comprise a cleaning step. This step may beparticularly useful when the polypropylene-based composition comprisesrecycled resins. Such a cleaning step may involve one or more of thegroup consisting of degassing by vacuum, the injection of supercriticalCO₂, and steam stripping. This cleaning step may further include afiltering step. The filtration may remove larger components (e.g.,larger than 30 microns, for example) from the molten polymer. Theconditions of the filtration depend upon the identity of the componentspresent in the melted mixture. Such a filtration process may beperformed in a manner consistent with those taught by U.S. Pat. Pub.2019/0366591, which is incorporated herein by reference.

The cleaning may be also used to remove volatile (lower molecularweight) components, such as residual peroxide and byproducts generatedby the chain scission reaction. Said steps may occur during the meltingand decreasing viscosity steps or in a subsequent or preliminary step.In one or more embodiments, the method includes removing at least one oflow molecular weight contaminants, byproducts, volatiles, or water, froma resin by exposing it to vacuum.

In some embodiments, the resulting product is pelletized.

Applications and Uses

One or more embodiments of the present disclosure relate to lowviscosity polypropylene-based compositions that are suitable formeltblowing. These compositions may be produced by the aforementionedprocesses. The meltblowing compositions may be meltblown, using veryhigh velocity air flow to draw a polymer melt extruding from a die, togive meltblown polymer fibers. One or more embodiments of the presentdisclosure are directed to a meltblown article that comprises aplurality of fibers formed from the low viscosity polypropylene-basedcompositions.

In one or more embodiments, the low viscosity polypropylene-basedcompositions that are suitable for meltblowing may have a very lowcontent of residual peroxides. In some embodiments, the low viscositypolymer composition may have a peroxide reside content of less than 1500ppm.

In one or more embodiments, the low viscosity polypropylene-basedcompositions that are suitable for meltblowing may have a viscosity oflower than 300 Pa·s. In one embodiment, the viscosity is in a range from10 to 300 Pa·s, such as 20 to 300 Pa·s. For example, the viscosity mayhave a lower limit of any of 10, 20, or 50 Pa·s, and an upper limit ofany of 50, 100, 150, 200, or 300 Pa·s.

In one or more embodiments, the low viscosity polypropylene-basedcompositions suitable for meltblowing processing have a melt flow rate,according to ASTM D1238 (230° C., 2.16 Kg), greater than 600 g/10 min,preferably greater than 1000 g/10 min, and most preferred greater than1,500 g/10 min.

In accordance with the present disclosure, the following procedure maybe applied to measure the viscosities of both the starting material andfinal product. The viscosity may be measured at a temperature of 180° C.using a parallel plates geometry with 25 mm of diameter and anoperational gap of 1 mm, with a defined stressor strain in the linearviscoelastic regime. A 100 Pa stress or 1% strain may be applied tooscillatory sweep from 0.1 to 625 rad/s. With this procedure, it may bepossible to use a single methodology to the measure both the startpolypropylene composition's viscosity as well as the low viscositypolypropylene-based compositions obtained.

In one or more embodiments, a melt blown fabric may be formed from aplurality of fibers formed from the low viscosity polypropylene-basedcompositions described herein. Such melt blown fabric may be nonwoven.

Further, it is also envisioned that the low viscositypolypropylene-based compositions of the present invention may also findapplicability as an additive in other polymer compositions, such as whena low viscosity polymer is desired. It is envisioned for example, thatthe low viscosity polypropylene-based compositions described herein maybe used as a viscosity modifier or as a binder or carrier in a highfilled compound.

Low viscosity polypropylene-based compositions according to the presentdisclosure may be used as a viscosity modifier in polymer compositionsto be applicable to different molding processes, including processesselected from extrusion molding, coextrusion molding, extrusion coating,injection molding, injection blow molding, inject stretch blow molding,thermoforming, cast film extrusion, blown film extrusion, foaming,extrusion blow-molding, injection stretched blow-molding, rotomolding,pultrusion, calendering, additive manufacturing, lamination, and thelike, to produce manufactured articles.

Low viscosity polypropylene-based compositions according to the presentdisclosure may also serve as a raw material for chemical recyclingprocesses, such as thermolysis: pyrolysis (thermal and catalyticdepolymerization), hydrogenation, hydrocraking, oxycracking,gasification, hydrothermal liquefaction and other suitable knownprocesses. In this case, it is preferred that the low viscositypolypropylene-based compositions are substantially obtained fromrecycled resins.

Low viscosity polypropylene-based compositions according to the presentdisclosure may also be used as a raw material for injection moldingprocesses and additive manufacturing (e.g. fused filament).

EXAMPLES Example 1

To illustrate the inventive process, polypropylene pellets were extrudedin a continuous process with an organic peroxide added as a first chainscission agent. In some examples, iron stearate (FeSt) was also added,as a second chain scission agent.

The PP is a 3-melt flow homopolymer, sold commercially by Braskem withtrade name FF030F2. The organic peroxide is 2,5-dimethyldi-tertbutylperoxyhexane, sold commercially by Nouryon with trade nameTrigonox 101. The Iron (iii) stearate (CAS: 555-36-2) was purchased fromAldrich.

Extrusion was conducted in a 21 mm Theysson twin screw extruder withL/D=36. Polypropylene pellets were fed into the feed throat of theextruder using a first feeder operating at a constant rate of 6 kg/hour.Iron stearate was added to the extruder using a second feeder to meteran iron stearate master batch concentrate. The iron stearate masterbatch was produced by extruding 2 wt. percent iron stearate powder withPP FF030F3 using the extrusion conditions shown in Table 1 (FeSt MB.)

Peroxide (“T101”) was injected directly into the barrel during extrusionusing a gear pump. The barrel segment upstream of the die was open toatmosphere to allow venting of volatiles.

Barrel temperatures are reported in Table 1. Nitrogen gas was fed intothe feed throat of the extruder. Screw speed was set to 250 rpm. Meltpressure and melt temperature were measured near the die. The extrudatemixtures were cooled in a water bath and collected as pellets.

TABLE 1 Feed concentration, Barrel temperatures, C. Melt PP feed wt %Zone6 Screw Torque, Melt temp, rate, T101 FeSt Zone1 Zone2 Zone3 Zone4Zone5 (die) speed % pressure C. kg/h CE1 0.1 0 189 201 209 249 250 230253 56 110 243 6 CE2 0.25 0 190 198 209 247 250 230 252 50 100 242 6 Ex10.1 0.1 189 198 209 243 259 239 252 69 119 243 6 Ex2 0.2 0.1 189 199 209244 249 230 251 59 110 240 6

Melt flow index and viscosity results are reported in Table 2 for theexamples described above and for a comparative control sample, which wasnot extruded. Melt flow was measured using ASTM procedure D1238.Viscosity was measured by a frequency sweep analysis in a shearrheometer operating at 180° C. Frequency sweep analysis (0.0628-628rad/s), oscillatory regime, was carried out in a rotacional rheometerDHR-3—TA Instruments, using a 25 mm Parallel plate geometry, gap of 1mm, stress of 10 Pa (determined in a previous test to be in the linearviscoelasticity regime) and a soaking time of 60 s, the results of whichare shown in FIG. 1.

One can note that, when using stearate together with the peroxidecompound, there is a significant decrease in the viscosity of thepolymer composition.

TABLE 2 Feed Concentration, wt % T101 FeSt Pellet MFR Viscosity at 0.1CE1 0.1 0 50 430 CE2 0.25 0 171 110 Ex1 0.1 0.1 84 270 Ex2 0.2 0.1 191160

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this invention. Accordingly, all such modifications areintended to be included within the scope of this disclosure as definedin the following claims. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents, but alsoequivalent structures. Thus, although a nail and a screw may not bestructural equivalents in that a nail employs a cylindrical surface tosecure wooden parts together, whereas a screw employs a helical surface,in the environment of fastening wooden parts, a nail and a screw may beequivalent structures. It is the express intention of the applicant notto invoke 35 U.S.C. § 112(f) for any limitations of any of the claimsherein, except for those in which the claim expressly uses the words‘means for’ together with an associated function.

What is claimed:
 1. A method for producing a low viscositypolypropylene-based composition, comprising: melting apolypropylene-based composition; decreasing a viscosity of thepolypropylene-based composition; and optionally, repeating the meltingand the viscosity decreasing steps to form a low melt viscositypolypropylene-based composition; wherein the melting and viscositydecreasing steps are performed in the presence of at least one freeradical generator and at least one pro-degradant stearate.
 2. The methodof claim 1, wherein the melting and viscosity decreasing steps areperformed at temperature that is equal to or less than 350° C.
 3. Themethod of claim 1, wherein the melting and viscosity decreasing stepsare performed at residence time of less than 2 min.
 4. The method ofclaim 1, wherein the polypropylene-based composition is a post-consumerresin, a post-industrial resin, petroleum based virgin polyolefin,biobased polyolefin or mixtures thereof.
 5. The method of claim 1,wherein the polypropylene-based composition comprises up to about 49 wt.% of an olefin-based resin.
 6. The method of claim 1, wherein thepolypropylene-based composition comprises up to about 49 wt. % of apolymer selected from polystyrene, ethylene-vinyl acetate polymer, otherolefin-based polymers and combinations.
 7. The method of claim 1,wherein the at least one free radical is added to thepolypropylene-based composition in an amount ranging from about 0.01 toabout 1.5 wt. %.
 8. The method of claim 1, wherein the at least one freeradical generator is a peroxide compound.
 9. The method of claim 8,wherein the peroxide compound is one or more of the group consisting of3-hydroxy-1,1-dimethylbutyl peroxyneodecanoate, a-cumylperoxyneodecanoate, 2-hydroxy-1,1-dimethylbutyl peroxyneoheptanoatea-cumyl peroxyneoheptanoate, t-amyl peroxyneodecanoate, t-butylperoxyneodecanoate, di(2-ethylhexyl) peroxydicarbonate, di(n-propyl)peroxydicarbonate, di(sec-butyl) peroxydicarbonate, t-butylperoxyneoheptanoate, t-amyl peroxypivalate, t-butyl peroxypivalate,diisononanoyl peroxide, didodecanoyl peroxide,3-hydroxy-1,1-dimethylbutylperoxy-2-ethylhexanoate, didecanoyl peroxide,2,2′-azobis(isobutyronitrile), di(3-carboxypropionyl) peroxide,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, dibenzoyl peroxide,t-amylperoxy 2-ethylhexanoate, t-butylperoxy 2-ethylhexanoate, t-butylperoxyisobutyrate, t-butyl peroxy-(cis-3-carboxy)propenoate,1,1-di(t-amylperoxy)cyclohexane,1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, OO-t-amyl O-(2-ethylhexyl) monoperoxycarbonate, OO-t-butylO-isopropyl monoperoxycarbonate, OO-t-butyl O-(2-ethylhexyl)monoperoxycarbonate, polyether tetrakis(t-butylperoxycarbonate),2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-amyl peroxyacetate, t-amylperoxybenzoate, t-butyl peroxyisononanoate, t-butyl peroxyacetate,t-butyl peroxybenzoate, di-t-butyl diperoxyphthalate,2,2-di(t-butylperoxy)butane, 2,2-di(t-amylperoxy)propane, n-butyl4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-amylperoxy)butyrate, ethyl3,3-di(t-butylperoxy)butyrate, dicumyl peroxide,a,a′-bis(t-butylperoxy)diisopropylbenzene,2,5-dimethyl-2,5-di(t-butylperoxy) hexane, di(t-amyl) peroxide, t-butyla-cumyl peroxide, di(t-butyl) peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, dicetil peroxi-dicarbonato,3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane, tert-butylperoxy2-ethylhexyl carbonate, tert-butyl-peroxide n-butyl fumarate(benzoate),dimyristoyl peroxydiicarbonate, 3,3,5,7,7-pentamethyl-1,2,4-trioxepane,tert-butyl hydroperoxide, bis(4-t-butylcyclohexyl) peroxydicarbonate,and 1,2,4,5,7,8-hexoxonane, 3,6,9-trimethyl-3,6,9-tris(ethyl and propylderivatives).
 10. The method of claim 8, wherein the peroxide compoundis selected from a group consisting of3,3,5,7,7-Pentamethyl-1,2,4-trioxepane, terc-butyl hydroperoxide, cumylhidroperoxide, t-amyl hidroperoxide, or mixtures thereof.
 11. The methodof claim 8, wherein the polypropylene-based composition is in thepresence of a further at least one free radical generator comprising anitroxide compound selected from a group consisting of2,2,5,5-tetramethyl-1-pyrrolidinyloxy,3-carboxy-2,2,5,5-tetramethyl-pyrrolidinyloxy,2,2,6,6-tetramethyl-1-piperidinyloxy,4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy,4-methoxy-2,2,6,6-tetramethyl-1-piperidinyloxy,4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy,bis-(1-oxyl-2,2,6,6-tetramethylpiperidine-4-yl)sebacate,2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl)monophosphonate,N-tert-butyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide,N-tert-butyl-1-dibenzylphosphono-2,2-dimethylpropyl nitroxide,N-tert-butyl-1-di(2,2,2-trifluoroethyl)phosphono-2,2dimethylpropylnitroxide, N-tert-butyl-(1-diethylphosphono)-2-methyl-propyl nitroxide,N-(1-methylethyl)-1-cyclohexyl-1-(diethylphosphono) nitroxide,N-(1-phenylbenzyl)-(1-diethylphosphono)-1-methyl ethylnitroxide,N-phenyl-1-diethylphosphono-2,2-dimethyl propyl nitroxide,N-phenyl-1-diethylphosphono-1-methyl ethyl nitroxide, N-(1-phenyl2-methyl propyl)-1-diethylphosphono-1-methyl ethyl nitroxide,N-tert-butyl-1-phenyl-2-methyl propyl nitroxide, andN-tert-butyl-1-(2-naphthyl)-2-methyl propyl nitroxide.
 12. The method ofclaim 1, wherein the at least one pro-degradant stearate is selectedfrom zinc stearate, tin stearate, iron (II) stearate, iron (III)stearate, cobalt stearate, manganese stearate, and any combinationsthereof.
 13. The method of claim 1, wherein the at least onepro-degradant stearate is added to the polypropylene-based compositionin an amount ranging from about 0.05 wt. % to 2.5 wt. %.
 14. The methodof claim 1, wherein the melting and viscosity decreasing steps areperformed in a residence time of less than 90 s.
 15. The method of claim1, wherein the melting and viscosity reducing steps are performed in acontinuous process.
 16. The method of claim 1, wherein the melting andviscosity reducing steps occur in an extruder.
 17. The method of claim1, wherein the extruder is twin screw extruder.
 18. The method of claim1, wherein the melting and reducing steps are repeated at least twotimes.
 19. The method of claim 1, wherein the repeated melting andreducing are performed in a continuous loop system.
 20. The method ofclaim 1, wherein the method further comprises a cleaning step selectedfrom one or more of the group consisting of degassing by vacuum,injecting supercritical CO₂, steam stripping and a filtering step.
 21. Alow viscosity polypropylene composition prepared according to the methodof claim
 1. 22. A low viscosity polypropylene based-composition preparedaccording to claim 21 wherein the polypropylene has a viscosity of lessthan 300 Pa·s at 180° C. and 0.1 rad/s.
 23. A melt blown fabriccomprising a plurality of fibers formed from the low viscositypolypropylene composition of claim
 21. 24. The melt blown fabric ofclaim 23, wherein the melt blown fabric is nonwoven.
 25. A method forproducing a melt-blown article, comprising: melt-blowing the lowviscosity polypropylene composition of claim 21.